Biochemical assay detection in a liquid receptacle using a fiber optic exciter

ABSTRACT

Biochemical assays that are performed in cuvettes and in the wells of multi-well plates and that utilize excitation and light emission as labels for detection are enhanced by an illumination and detection system that supplies excitation light through an optical fiber that transmits excitation light from an excitation light source to the cuvette or well. Emission light produced by the excitation is then collected by a collimating lens and converted to a signal that is compiled by conventional software for analysis. The optical fiber and collimating lens can either be on the same side of the receptacle (generally the open side) or on opposite sides, i.e., one above and the other below. When the optical fiber and the collimating lens are both on the open side of the receptacle, they are arranged such that the direction of travel of the excitation light and the direction along which the emission light is collected are not coaxial, and preferably both are at an acute angle to the axis normal to the mouth of the receptacle. Illumination systems are also disclosed in which a ultraviolet, visible, or near-infrared light source is optically coupled to an optical fiber.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefits of co-pending U.S.provisional patent applications Nos. 60/325,855 and 60/325,876, bothfiled on Sep. 27, 2001, for all purposes legally capable of being servedthereby. The contents of each of these provisional patent applicationsare incorporated herein by reference in their entirety, as are all otherpatent and literature references cited throughout this specification.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention resides in the field of biochemical assaysperformed in receptacles such as cuvettes or the wells of multi-wellplates such as MICROTITER® plates, and particularly in obtaining theassay results by optical excitation of the receptacle contents anddetection of the emissions resulting from the excitation.

[0004] 2. Description of the Prior Art

[0005] Fluorescence and other optical signals are widely used inbiochemical assays, particularly as a label in distinguishing testspecies that have demonstrated a sought-after property or characteristicin the assay from those that have not. Assays utilizing optical signalsare frequently performed in liquid or fluid media retained in a samplereceptacle, and optical measurements are performed either on speciessuspended in the liquid media or on species adhering to the walls of thereceptacle, such as species immunologically bound to the walls ofmicroplate wells or cells plated to the bottoms of cuvettes.Instrumentation in current use for measuring fluorescence include alight source and a lens system for focusing a beam into the samplereceptacle, and an optical system for collecting and processing theemission light that results from the excitation. The two frequentlyinterfere with each other, however, resulting in a loss of assaysensitivity.

[0006] In one type of excitation and emission detection system, apierced mirror, which is either flat or elliptical, is used for bothdirecting the excitation light to the sample receptacle and collectingthe emission light that is produced. Pierced-mirror systems have limitedsensitivity, however, since the need to optimize the collection of theweaker emission light requires compromises that result in loss of muchof the excitation light. As a result, these devices suffer from areduced intensity due to restricted aperture considerations and to themisdirection of a portion of the excitation light.

[0007] Other systems use a dichroic mirror to separate the excitationand emission light which are otherwise along a common path. The use of adichroic mirror simplifies the optical path and instrument layout, butefficient separation of the emission light from the excitation lightrequires an expensive optical filter and a reduction in the signallight. Dichroic mirror systems are principally used in microscopy wherelight is abundant, rather than in systems where trace amounts offluorophore are detected with low levels of emission light.

SUMMARY OF THE INVENTION

[0008] The present invention resides in illumination and detectionsystems for biochemical assays performed in small liquid receptaclessuch as cuvettes, small test tubes, or the wells of a multi-well plate.The receptacle is illuminated with a divergent beam of excitation lightfrom an optical fiber, and emission light generated in the receptacle asa result of the excitation is collected, preferably without the use ofan optical fiber, by a collimating lens and converted by a detector to asignal that can be quantified, recorded, and otherwise processed byconventional instrumentation components. When the receptacle is one wellof a multi-well plate such as a MICROTITER® plate, further signals areobtained by rastering either the plate or the optical system untildetection has been performed on all wells of the plate. This system isapplicable to any receptacle in which an assay is performed thatutilizes a label that emits a signal upon optical excitation. Preferredlabels are fluorophores and fluorescent emissions, but the inventionextends as well to phosphors and other types of optically excitablelabels known to those familiar with biochemical assays.

[0009] In preferred embodiments of the invention, the optical system isarranged such that the direction of travel of the excitation light andthe direction along which the emission light is collected are twodifferent directions, i.e., the two paths do not have a common axis. Theoptical fiber is configured to illuminate the test area either byepi-illumination (i.e., directing excitation light to the receptaclecontents through the open mouth of the receptacle and collectingemission light through the open mouth as well) or by trans-illumination(using a light-transmissive receptacle or one with a light-transmissivefloor, and either directing excitation light to the receptacle fromabove and collecting emission light from below through thelight-transmissive floor, or directing excitation light from belowthrough the light-transmissive floor and collecting emission light fromabove). In multi-well plates, illumination and emission detection canlikewise occur at opposite sides of the plate, either by illuminatingfrom below (the underside of the plate) and collecting emission fromabove (through the mouth of a well), or by illuminating from above andcollecting emission from below. In systems utilizing epi-illumination,the optical fiber and the direction along which the emission light iscollected are not coaxial, instead forming an angle to each other. Intrans-illumination as well, the optical fiber and the optical path usedfor collection of the emission light are in a non-coaxial arrangement.Preferred optical fibers for use in this invention are those thatproduce a divergent angle sufficient to illuminate the entire receptacleincluding all of the test materials contained in the receptacle, and toilluminate only that receptacle, i.e., without illuminating materials inneighboring receptacles.

[0010] Preferred excitation light sources are those supplyingultraviolet, visible, or near-infrared light, optically coupled with theoptical fiber so that substantially all of the light from the lightsource enters the fiber for transmission to the receptacle interior.This will result in substantially no loss of intensity between the lightsource and the receptacle. The optical fiber itself may be a simplefiber or one that includes such elements as a collimator or opticalfilter, or a collimator-filter-collimator assembly, to process the lightin various ways that will enhance its use for particular applicationsand assays.

[0011] Systems in accordance with this invention offer numerousadvantages over the prior art. By separating the excitation and emissionlight paths, systems in accordance with this invention limit theexcitation and emission optics to a single function each, therebypermitting individual optimization of these two optical systems. Inepi-illumination systems, little of the excitation light is detected inthe emission light path and a maximal signal-to-noise ratio is achieved,particularly when the illumination fiber and the emission collectionoptics are at different angles relative to the normal axis. When thesystem is used on multi-well plates, only a single well is illuminatedby the optical fiber and emission is collected from that wellindividually, thereby eliminating crosstalk and maximizing the signal ofthat well. This leads to maximal signal collection and superiorperformance for any given level of detection and sensitivity.Furthermore, excitation systems of this invention require no additionallenses or other optical elements between the excitation fiber and theassay receptacle, and can thus avoid the losses in light intensity thatare often caused by these additional elements. In aspects of thisinvention that are directed to an optical fiber optically coupleddirectly to an LED or SLD light source, the coupled product isinexpensive, durable, and compact, and delivers bright light whilegenerating minimal heat. This simplified yet highly efficient designpresents advantages for packaging, cost and size reduction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a diagram of an excitation and detection system for amulti-well plate utilizing the features of the present invention.

[0013]FIG. 2 is a diagram of an excitation system for use in conjunctionwith the excitation and detection system of FIG. 1, using an LED or SLDlight source optically coupled to the fiber and an optical filter on theoutput end of the fiber.

[0014]FIG. 3 is a diagram of a second excitation system for use inconjunction with the excitation and detection system of FIG. 1, alsousing an LED or SLD light source optically coupled to the fiber and anoptical filter on the output end of the fiber.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0015] Receptacles in which bioassay detection can be performed by useof the present invention include cuvettes, small test tubes, wells ofmulti-well plates, and any variety of vessels capable of containing thecomponents used in performing biochemical assays. Examples of multiwellplates are MICROTITER® plates, as well as plates bearing differentdesignations but generally containing either a row of wells or atwo-dimensional rectangular array of wells. The most commonly usedmulti-well plates are those with a 96-well (12×8) array. Others have6-well, 12-well, 48-well, 384-well, and 1536-well arrays. Typical welldiameters or widths are from about 4 mm to about 40 mm, and preferablyfrom about 4 mm to about 11 mm. The emissions to be generated anddetected in the practice of this invention can arise from liquidretained in the receptacle, from substances suspended in the liquid, orfrom substances adhering to the receptacle walls.

[0016] The excitation system of this invention may contain any of avariety of different types of light sources. Examples are broadbandlight sources such as xenon flash lamps, quartz halogen lamps,light-emitting diodes (LEDs), vertical cavity surface-emitting lasers(VCSELs), superluminescent diodes (SLDs), and narrowband sources such assingle or multiple discrete wavelength lasers. In preferred systems, thelight source is optically coupled to the optical fiber. For pointsources of light or sources such as solid state sources that are nearlypoint sources, optical coupling may be achieved by proximity coupling.Otherwise, a coupling lens or lens system that will transmitsubstantially all of the light from the light source to the fiber can beused. The system can also include an optical excitation filter, amonochromator, or a tunable acousto-optic filter. The optical fibertransmits light from the light source to the receptacle to excite eithera single label or multiple labels that are present in the receptacle.Emission light resulting from the excitation is collected by acollimating lens system which directs the light to a detector,optionally first passing through an optical emission filter, amonochromator, or a tunable acousto-optic filter. Examples of suitabledetectors are photomultiplier tubes, microchannel plates, silicon PINdiodes, avalanche photodiodes (APDs), CCD detectors, and CMOS detectors.

[0017] The optical fiber is either straight or tapered along its length.The choice of fiber may vary with the particular type of receptacle towhich the light is directed. A multi-mode fiber with cladding and outerbuffer coating is preferred, particularly one with a divergence anglesuitable for filling the interior of the receptacle. Such fibers arecommercially available from various suppliers well known to those in theindustry. One such supplier is 3M Company, St. Paul, Minn., USA, andanother is Polymicro Technologies, LLC, Phoenix, Ariz., USA.

[0018] The optical fiber can have either a standard tip or a shaped tipon either or both of its ends, or a combination of both. In certainembodiments of the invention, the delivery end preferably has a shapedtip such as a concentrator cone tip. The tip may also have an integrallens. The divergence angle at the distal tip is preferably within therange of about 10 degrees to about 60 degrees, most preferably fromabout 10 degrees to about 20 degrees. In terms of the numerical aperture(the sine of the divergence angle θ), the preferred range is from about0.17 to about 0.94, and most preferably from about 0.17 to about 0.34.For MICROTITER® plates, a presently preferred numerical aperture is 0.22(a divergence angle of 12.7 degrees). Optical fibers with shaped tips asdescribed in this paragraph are available from Polymicro Technologiesreferenced above.

[0019] The tip of the optical fiber is preferably placed very close tothe mouth of the receptacle, particularly in the case of receptaclesthat are wells in multi-well plates where illumination of neighboringwells is sought to be avoided. Preferably, the fiber tip is placedwithin 1 mm to 10 mm of the mouth of the well.

[0020] The vessel in which the receptacle is formed can be opaque orlight-transmissive, and light-transmissive vessels can be translucent ortransparent. When a light-transmissive vessel is used, illumination ofthe receptacle interior with excitation light can be achieved from theunderside of the vessel, i.e., through the light-transmissive bottom ofthe vessel (“trans-illumination”). The angle of incidence of theexcitation light is defined relative to the axis normal to the mouth ofthe receptacle, and this angle is not critical and may vary. Likewise,the direction along which the collimating lens collects the emissionlight can vary. In systems where trans-illumination is used, it ispreferred that the emission light be collected along an acute anglerelative to the axis. Preferred such angles are at least about 5° andmost preferably from about 5° to about 15°. In systems involvingepi-illumination, the optical fiber and the direction along which theemission light is collected are non-coaxial, and it is preferred thatthe fiber and the emission collection direction each form angles(relative to the axis) of from about 5° to about 60°, and morepreferably from about 5° to about 25°. When the receptacle is amulti-well plate, a presently preferred angle for the optical fiber(relative to the axis) in epi-illumination systems is 10°, with theemission collection path at 15° relative to the fiber, while intrans-illumination systems a presently preferred angle for the opticalfiber is 5-10° (relative to the axis), with the emission collection pathalong the axis itself.

[0021] Of the various types of light sources that can be used in thepractice of this invention, broadband LEDs are preferred. This and othertypes of light source can also include a phosphor or other broadbandconversion element upstream of the coupling to the fiber. The conversionelement can be a coating on the light source, or it can be incorporatedinto the plastic packaging of the light source or in a gel or otherdiscrete closed package. As a further alternative, the conversionelement can be intagliated into the end of the fiber itself.

[0022] The optical coupling between the light source and the opticalfiber can be achieved by a focusing lens or lens system located betweenthe light source and the optical fiber, or by direct coupling of theoptical fiber to the light source. Examples of focusing lens systems area ball lens, a pair of microscope objectives, and a condenser pair ofplano convex lenses. Proximity coupling, i.e., direct coupling of thefiber to the light source, is preferred. LEDs and SLD's, which arereadily available from commercial suppliers, can be readily modified byremoving the lens system supplied by the manufacturer and placing theflat fiber end very close to, and preferably in direct secured contactwith, the glowing LED itself. An optically clear cement with lowautofluorescence can be used. Examples of such a cement are NorlandOptical Cement NOA 73 and NOA 61, Norland Products, Inc., Cranbury,N.J., USA. Alternatives to cements are gels or oils that are opticallyclear. To stabilize the coupling, the LED or SLD and the fiber end canbe encased in a metal tube, a straight tip (ST) connector, or any otherpackaging, with one end of the connector joined to the LED or SLD andthe other to the optical fiber.

[0023] While the novelty-defining concepts and features of the inventioncan be implemented in many different configurations and arrangements, aconvenient way to achieve an understanding of these features is to studyindividual systems within the scope of the invention. Such system aredepicted in the Figures.

[0024] The system shown in FIG. 1 is arranged for signal generation anddetection in a multi-well plate 11 such as a MICROTITER® plate, eachwell 12 of which is partially filled with liquid components of abiochemical assay. The contents of each well have been treated with anyof various fluorochrome dyes or probes or any other labels that whenirradiated with an excitation light beam respond by producing emissionlight. The well diameter can be less than 4 mm or greater than 36 mm indiameter, depending on the number of wells in the plate. The plate 11 isheld by a holding fixture (not shown) which moves or rasters the platein the x and y directions within a plane that is transverse to thedirection of the optical paths through which excitation and emissioncollection are performed. This rastering movement enables the system tocapture signals sequentially from the entire array of wells. As analternative arrangement, the plate can be held stationary and the opticsmade movable in the x and y directions across the sample surface.

[0025] An excitation light source 14, which may be a broadband sourcesuch as for example a xenon lamp, a quartz halogen lamp, an LED, an SLD,or a narrow band source such as for example a single or multiplediscrete wavelength laser, illuminates a collimating lens 15.Alternatively, two or more discrete lasers can be used simultaneouslywith a single fiber. The collimated light emerging from the collimatinglens 15 passes through an optical excitation filter 16 on amulti-position filter wheel 17. The filter wheel permits the selectionof particular excitation wavelengths from a variety of wavelengths, andits rotation and position can be controlled by software appropriatelyadapted to particular experimental protocols. As alternatives to theoptical excitation filter, a monochromator or a tunable acousto-opticfilter may be used. A second lens 18 focuses the light and couples itinto either of two optical fibers 19, 20. The fibers terminate in fiberholders 21, 22, respectively, the output end of each fiber holder beingpositioned in close proximity to a well 12 on the plate 11. These twooptical fibers offer alternative means of providing excitation light tothe well, one fiber 21 delivering the excitation light to the top sideof the plate through the open mouth 23 of the well for epi-illuminationand the other fiber 22 delivering the excitation light to the underside24 of the plate for trans-illumination of the well through the plateitself.

[0026] In the system shown in FIG. 1, no additional lenses or optics arelocated between the fiber holders 21, 22 and the well plate 11. Lightfrom the fiber tip 23 produces a cone-shaped beam of excitation lightwhich fills the well 12. The divergence of the light cone can also becontrolled or modified by either specialized cutting, polishing, orangling of the fiber end. Optionally, a mask 24 can be positioned abovethe sample to further assure that the well of interest does not receiveany stray excitation or emission light from neighboring wells or fromdust or other contaminants.

[0027] The emission light that the well 12 emits upon excitation iscollected by a collimating lens 31, and the collimated emission lightpasses through an optical emission filter 32 on a multi-position filterwheel 33. Alternatively, a monochromator or tunable acousto-optic filtercan be used in place of the optical emission filter 32. A second lens 34then focuses the collimated light through an aperture 35 to controlstray light and onto a light detector 36. Examples of suitable lightdetectors are photomultiplier tubes, silicon PIN diodes, avalanchephotodiodes (APDs), CCD detectors, and CMOS detectors. The detector 36registers the emission light intensity and sends an output signal to arecorder or to processing and control electronics 37.

[0028] These systems and other systems within the scope of thisinvention are readily adaptable to achieve signal generation andprocessing by Time-Resolved Fluorescence. This is accomplished forexample by using a flashlamp, an LED, or an SLD as the light source,imposing a controlled delay time between a flash of the light source andthe signal collection, and allowing for programmable variable signalcollection integration time. The only modifications needed to achievethis are modifications of the software and electronics, and suchmodifications will be readily apparent to those skilled in the art ofTime-Resolved Fluorescence.

[0029] Although not shown in the drawings, the system can include two ormore optical excitation fibers arranged either in a linear array or anx-y (two-dimensional) array rather than in a single fiber. Eachindividual excitation fiber is associated with a separate collectionchannel, and the entire fiber array can be moved across the well plate,or the plate moved relative to the fiber array, and in either casesignals are obtained from all wells of the plate in a shorter span oftime than a single fiber.

[0030] Examples of illumination systems in accordance with thisinvention utilizing an LED or SLD light source are shown in FIGS. 2 and3.

[0031] The system of FIG. 2 includes an LED or SLD source 41, preferablya white light LED or SLD, directly coupled to the flat end of an opticalfiber 43 through an optical cement such as those described above. Thecoupling is surrounded by an epoxy potting compound 42 or a ring ortube. Light emerging from the LED or SLD is efficiently collected by theoptical fiber 43 and transmitted to a fiber-optic device 44, whichconsists of a first fiber collimator for the light emerging from the LEDor SLD, an optical bandpass filter, and a second fiber collimator forthe light emerging from the optical bandpass filter. The filter caneither be a single optical bandpass filter or multiple filters mountedon a wheel or slide, allowing the user, either manually or by automatedmeans, to select a particular filter and thereby excite a specificfluorophore. The light emerging from the second fiber collimator returnsto the fiber for delivery from the fiber tip 45 to a test region 46 on amulti-well plate.

[0032] The system of FIG. 3 has the same components as the system ofFIG. 2 except that the sealant and packaging 42 of FIG. 1 are replacedby a compact lens or lens system 52.

[0033] The foregoing descriptions are offered primarily for purposes ofillustration. Further modifications, variations and substitutions thatstill fall within the spirit and scope of the invention will be readilyapparent to those skilled in the art.

What is claimed is:
 1. Apparatus for generating and detecting an opticalsignal from the contents of a liquid receptacle resulting from abioassay performed therein, said apparatus comprising: an excitationlight source, an optical fiber arranged to transmit excitation lightfrom said excitation light source to said receptacle with a divergentbeam, and a collimating lens arranged to collect emission light fromsaid receptacle; and detection means for receiving emission lightcollected by said collimating lens and for generating a signalrepresentative of said emission light thus collected.
 2. Apparatus inaccordance with claim 1 in which said optical fiber has a divergenceangle of from about 10° to about 60°.
 3. Apparatus in accordance withclaim 1 in which said optical fiber has a divergence angle of from about10° to about 20°.
 4. Apparatus in accordance with claim 1 in which saidoptical fiber has a numerical aperture of from about 0.17 to about 0.34.5. Apparatus in accordance with claim 1 in which said receptacle has anopen mouth, said optical fiber is arranged to direct said excitationlight through said open mouth, and said collimating lens is arranged tocollect said emission light through said open mouth.
 6. Apparatus inaccordance with claim 5 in which said collimating lens is arranged tocollect said emission light along an emission collection path that isnot coaxial with said optical fiber.
 7. Apparatus in accordance withclaim 6 in which said open mouth defines an axis normal thereto, andsaid optical fiber and said emission collection path each form an angleof from about 5° to about 60° relative to said axis.
 8. Apparatus inaccordance with claim 6 in which said open mouth defines an axis normalthereto, and said optical fiber and said emission collection path forman angle of from about 5° to about 25° relative to said axis. 9.Apparatus in accordance with claim 1 in which said receptacle has alight-transmissive floor and an open mouth opposite saidlight-transmissive floor, said optical fiber is arranged to transmitlight to the contents of said receptacle through one of saidlight-transmissive floor and said open mouth, and said collimating lensis arranged to collect said emission light through the other of saidlight-transmissive floor and said open mouth.
 10. Apparatus inaccordance with claim 9 in which said receptacle defines an axis normalto said open mouth, and said collimating lens is arranged to collectsaid emission light at an angle of at least about 5° relative to saidaxis.
 11. Apparatus in accordance with claim 9 in which said receptacledefines an axis normal to said open mouth, and said collimating lens isarranged to collect said emission light at an angle of from about 5° toabout 15° relative to said axis.
 12. Apparatus in accordance with claim1 in which said excitation light source is a UV, visible, or near-IRlight source and is optically coupled to said optical fiber. 13.Apparatus in accordance with claim 12 in which said excitation lightsource is a light-emitting diode and said optical fiber is secured to,and in direct contact with, said diode, either by direct coupling orthrough a member selected from the group consisting of an opticallyclear adhesive, gel or oil.
 14. Apparatus in accordance with claim 12 inwhich said UV, visible, or near-IR light source is a light-emittingdiode and is optically coupled to said optical fiber through a lenssystem directing all from said diode into said optical fiber. 15.Apparatus in accordance with claim 1 in which said liquid receptacle isa well of a multi-well plate, and said apparatus further comprises meansfor rastering either said multi-well plate relative to said opticalfiber and said collimating lens or said optical fiber and saidcollimating lens relative to said multi-well plate until light from saidexcitation light source has illuminated, and emission light has beencollected from, all wells of said multi-well plate.
 16. A method forgenerating and detecting an optical signal from the contents of a liquidreceptacle resulting from a bioassay performed in said receptacle, saidmethod comprising: (a) illuminating the contents of said receptacle withlight from an excitation light source through an optical fiber directinga divergent beam at said receptacle; and (b) collecting emission lightfrom said receptacle by a collimating lens and directing emission lightthus collected to a detector.
 17. A method in accordance with claim 16in which said optical fiber produces a divergence angle of from about 10degrees to about 60 degrees.
 18. A method in accordance with claim 16 inwhich said optical fiber produces a divergence angle of from about 10degrees to about 20 degrees.
 19. A method in accordance with claim 16 inwhich said optical fiber has a numerical aperture of from about 0.17 toabout 0.34.
 20. A method in accordance with claim 16 in which saidreceptacle has an open mouth and said method comprises illuminating thecontents of said receptacle through said open mouth and collecting saidemission light from said receptacle through said open mouth.
 21. Amethod in accordance with claim 20 in which step (b) comprisescollecting said emission light from said receptacle along an emissioncollection path that is not coaxial with said optical fiber.
 22. Amethod in accordance with claim 21 in which said receptacle defines anaxis normal to said open mouth, and said optical fiber and said emissioncollection path each form an angle of from about 5° to about 60°relative to said axis.
 23. A method in accordance with claim 21 in whichsaid receptacle defines an axis normal to open mouth, and said opticalfiber and said emission collection path form an angle of from about 5°to about 25° relative to said axis.
 24. A method in accordance withclaim 16 in which said receptacle has a light-transmissive floor and anopen mouth opposite said light-transmissive floor, step (a) comprisesdirecting said divergent beam through one of said light-transmissivefloor and said open mouth, and step (b) comprises collecting saidemission light through the other of said light-transmissive floor andsaid open mouth.
 25. A method in accordance with claim 24 in which saidreceptacle defines an axis normal to said open mouth, and step (b)comprises collecting said emission light along an emission collectionpath the forms an angle of 0° to about 15° relative to said axis.
 26. Amethod in accordance with claim 16 in which said receptacle is a memberselected from the group consisting of a cuvette and a well of amulti-well plate.
 27. A method in accordance with claim 16 in which saidreceptacle is a well of a multi-well plate, said well having an internaldiameter of from about 4 mm to about 40 mm.
 28. A method in accordancewith claim 16 in which said receptacle is a well of a multi-well plate,said well having an internal diameter of from about 4 mm to about 11 mm.29. A method for generating and detecting optical signals from aplurality of biochemical assays performed in individual wells of amulti-well plate, said method comprising: (a) illuminating the contentsof a single well with light from an excitation light source through anoptical fiber directing a divergent beam at said well; (b) collectingemission light from said well by a collimating lens and directingemission light thus collected to a detector; and (c) rastering eithersaid multi-well plate relative to said optical fiber and saidcollimating lens or said optical and said collimating lens relative tosaid multi-well plate until light from said excitation light source hasilluminated, and emission light has been collected from, all wells ofsaid multi-well plate.